Radiation diagnostic system, also known as X-ray television system, X-ray CT (Computer Tomography) system, etc., are known prior art.
The conventional X-ray television system converts an X-ray transmitted image obtained by irradiating X-rays onto a subject to a bright optical image by means of an X-ray image intensifier that picks up this optical image by means of a video camera. Accordingly, with such an X-ray television system, a two-dimensional pictorial image could be obtained, but a three-dimensional pictorial image (images of many layers or layered surfaces) cannot be obtained. In this case, the X-ray image intensifier has a dimension of 14 inches (diameter of about 35 cm) even at the maximum. For this reason, a large visual field cannot be provided. For example, it was impossible to cover the entirety of the breast. In addition, there was also the problem that the image distortion is large because such an intensifier is apt to be affected by vibration or geomagnetism.
On the other hand, the conventional X-ray CT system is adapted to allow an X-ray source and one-dimensional array sensor which are caused to be in one body to turn round a subject to form an image of each layer from one-dimensional transmitted images in plural directions obtained from the one-dimensional array sensor, e.g., by the so-called convolution back projection method (Reference Literature: L. A. Feldkamp, L. C. Davis, and J. W. Kress, "Practical cone-beam algorithm", J. Opt. Soc. Am. A/Vol. 1, No. 6 612-619/June 1984), or the Fast Fourier Transform (FFT) method. Accordingly, with such an X-ray CT system, only images of two or three layers, for example, could be obtained at best every one rotation. In order to obtain images of many layers, e.g., images of 128 layers, when it is assumed to take five seconds per each layer, it would take 640 (=5.times.128) seconds. Accordingly, such X-ray CT system is insufficient as a clinical system for patients, and there was also the problem that a quantity of X-ray exposure becomes vast. In other words, when a quantity of exposure is taken into consideration, the resolution in a body axis direction connecting the head and the foot of a patient could not be so much high.
As stated above, in the conventional X-ray television system, there is the problem that a three-dimensional pictorial image cannot be provided, or the like. On the other hand, in the conventional X-ray CT system, a three-dimensional pictorial image can be obtained, but there were the problems that it takes much time, a quantity of X-ray exposure is large, the resolution in a body axis direction is poor, and the like.
This invention has been made in view of such actual circumstances, and its object is to provide a radiation diagnostic system capable of obtaining, in a short time, a three-dimensional pictorial image having less distortion and a high resolution in a broad region.